1. Field of the Invention
The present invention relates to a lens barrel of a camera constructed so that a plurality of lens frames each having a photographic lens group are movable along an optical axis.
2. Related Art Statement
In recent years, in widespread compact zoom cameras, a zoom lens barrel advances and retracts so as to cover a photographic range from a wide angle position to a telephoto position. Such a zoom lens barrel has been put into practical use. In order to become more compact in size while being carried, the zoom lens barrel can move from a photographic position such as the wide angle position or the telephoto position to a collapsing position in which the zoom lens barrel is received in a camera body.
Furthermore, in recent years, higher zoom magnification is desired. Accordingly, a difference between the length of the lens barrel at the wide angle position or the collapsing position and the length of the lens barrel at the telephoto position becomes larger. In order to cope with this situation, serving as the structure of a lens frame assembly which can extend longer, a zoom lens barrel composed of many lens frames, namely, having a multistage lens frame structure is needed.
In this kind of zoom lens barrel, generally, a plurality of lens frames holding photographic lens groups are independently movable along an optical axis. Serving as a zoom lens barrel having such a multistage lens frame structure, for example, there is a four-stage zoom lens barrel instructed by combining two single annular frames with a double frame with a double structure including a frame member having a cam or a helicoid and a straight frame having a straight guide.
The zoom lens barrel comprises a first-stage stationary frame fixed to and held by a camera body, a second-stage rotary frame and a movable frame in the rotary frame, a third-stage cam frame and a float key in the cam frame, and a fourth-stage first lens frame. The zoom lens barrel further comprises a second lens frame and a third lens frame which are received in the cam frame, and an advancing gear.
The first lens frame, the second lens frame, and the third lens frame hold a first lens group, a second lens group, and a third lens group along an optical axis of a lens of the present lens barrel, respectively. Each lens group comprises a plurality of photographic lenses.
In the zoom lens barrel having the above configuration, a rotating force is transmitted from the advancing gear to the rotary frame, which is rotatably held in the stationary frame. Thus, the movable frame is first advanced relative to the rotary frame. Then, the cam frame, which is engaged with a through cam of the movable frame and the straight groove of the rotary frame, is also advanced. Consequently, the first lens frame which is engaged with the cam groove in the cam frame, the second lens group, and the third lens group are advanced together with the float key in the cam frame. In this case, in some cases, the first lens frame and the third lens frame are moved together upon zooming in order to simplify the mechanism and provide precision.
For the type of zoom lens barrel in which the first lens frame and the third lens frame are moved together, when the performance of the camera is considered, in any of the multistage advancing type zoom lens barrels, the positions of the first lens frame and the third lens frame with respect to a film plane are important. Particularly, it is desirable to position the third lens group, which is closer to the film plane, with high precision.
In the above multistage zoom lens barrel, the structure of the lens frame assembly is complicated and the weight of the entire zoom lens barrel is heavy. On the other hand, however, further reduction in size and weight of the compact zoom camera is demanded. For the purpose of satisfying the demands, it is desired to realize the structure of a lens frame assembly with simple components in which first and third lens frames are positioned with high precision in a simple configuration and a space between the first and third lens frames can be reduced upon collapsing.
For this kind of related arts, a zoom lens barrel disclosed in Japanese Unexamined Patent Application Publication No. 11-64714 is known. According to the proposal, in the zoom lens barrel, a plurality of lens groups constituting a photographic optical system are moved interlockingly along an optical axis to perform the zooming operation in a predetermined range. The zoom lens barrel comprises: a first lens group supporting cylinder for supporting a first lens group; a second lens group supporting cylinder for supporting a second lens group; a cam cylinder for supporting the first lens group supporting cylinder and the second lens group supporting cylinder so that they are movable relative to each other along the optical axis; and driving cam means having a cam including a first cam area to move the first lens group supporting cylinder along the optical axis and a second cam area to move the second lens group supporting cylinder along the optical axis, the cam being formed so that a part of the first cam area and the second cam area is shared by the first lens group supporting cylinder and the second lens group supporting cylinder during the zooming operation in the predetermined range.
Thus, the accomplishment of the following object is attempted. According to the object, a movable range of each lens group can be sufficiently maintained without increasing the size of the cam cylinder and the entire length of the zoom lens barrel upon collapsing can be shorter than that of the conventional one.
However, the zoom lens barrel disclosed in Japanese Unexamined Patent Application Publication No. 11-64714 is constructed in such a manner that a zoom pin, whose base end constitutes a retaining portion for preventing slipping from a thrust receiving hole, is inserted through the thrust receiving hole formed in an external flange at the front end of the third lens frame. Accordingly, the zoom lens barrel has the following disadvantages. When a first lens frame and a third lens frame are positioned, it is difficult to position them with high precision. The zoom lens barrel requires a space for the thrust receiving hole and a length as long as the zoom pin from the viewpoint of the structure. Therefore, it is difficult to further reduce the length of the zoom lens barrel upon collapsing. Furthermore, when a manufacturing process is considered, the process is complicated because the operation of forming the thrust receiving hole and the operation of attaching the zoom pin are needed, resulting in high cost.
It is an object of the present invention to accomplish positioning of first and third lens frames with high precision using simple components and to realize compactness, a simple manufacturing process, and a reduction in manufacturing cost.
In brief, a lens barrel according to the present invention includes:
a first lens group;
a first frame member supporting the first lens group;
a second lens group;
a second frame member supporting the second lens group, the second frame member being movable forward and backward relative to the first frame member along an optical axis;
a cam follower provided for the first frame member;
a cam frame member having a cam groove which is engaged with the cam follower to permit the first frame member to be movable forward and backward along the optical axis;
a contact portion provided for the second frame member, the contact portion being capable of coming into contact with the cam follower; and
a pushing member for pushing the second frame member in a direction in which the cam follower comes into contact with the contact portion,
wherein when the second frame member is pushed by the pushing member, the contact portion comes into contact with the cam follower to restrict a position of the second lens group with respect to the first lens group.
The object and advantages of the present invention will become further apparent from the following detailed explanation.